Abstract:
Leptocybe invasa is an invasive gall wasp and pest of Eucalyptus trees, which has become widely distributed in Africa, Asia, Europe and the Americas. Several other wasp species have been found to co-occur in L. invasa-induced galls. In South Africa, this includes an introduced biological control agent, Selitrichodes neseri; two known, accidentally introduced parasitoids, Megastigmus zebrinus and Quadrastichus mendeli; and M. pretorianensis, whose role in the gall is uncertain. In addition to the gall associates, a second lineage of L. invasa or cryptic species was discovered in South Africa in 2015. To determine the distribution and prevalence of these species across South Africa, a national monitoring scheme was initiated. Galled Eucalyptus material was collected at infested sites and emerging adults were collected and identified. Morphology, DNA barcoding and polymerase chain reaction (PCR) Restriction Fragment Length Polymorphism analyses were used to differentiate between the species and lineages. Results from the first two sampling periods indicated that L. invasa lineage A has spread throughout South Africa while lineage B had a more limited distribution in the country. Subsequent samples recorded the further spread of L. invasa Lineage B, which now occurs in all provinces sampled. The Leptocybe lineages were found to co-occur on individual trees, increasing the potential for admixture. From the Eucalyptus genotypes sampled, there was no indication of differences in host association between the Leptocybe lineages. Selitrichodes neseri, M. zebrinus and M. pretorianensis were present throughout South Africa and emerged from trees that contained both Leptocybe lineages, but their frequency varied with site. This study will inform future distribution of parasitoids as well as monitoring of potential changes in plant host resistance, admixture and parasitoid resistance in future.
